Computer Assisted Surgery (CAS) tools have been developed using optical motion capture to convert three-dimensional (3D) locations of passive reflective fiducial markers into the 3D pose of surgical instruments relative to user-selected anatomic landmark points. CAS may be used as a quantitative intra-operative measurement system to assess alignment performance. CAS systems, however, were not designed for rigorous analysis required to validate intra-operative performance. For example, CAS read-outs have been commonly limited to 1 mm and 0.5-degree increments of precision, and absolute accuracy to anatomic landmarks has been difficult to validate. Also, CAS alignment was limited by the operator's ability to consistently identify anatomic landmark points. CAS anatomic landmarks have been limited to those that could be safely and quickly accessed physically on live patients. CAS systems were not primarily intended as research tools, but as tools to assist in a clinical procedure. The level of precision of CAS systems may be useful for surgeons making informed intra-operative decisions, but may not be sufficient to distinguish subtle differences between alignment methods.